In order to permit paint manufacturers to offer an almost limitless selection of colors to their retail and trade customers, colorant dispensing machines have been developed to permit the so-called "in-store" tinting of pigmented or clear bases at the point of sale. Advanced colorant dispensing machines have been developed that include up to twelve, or more, colorant reservoirs into which each colorant is poured, and a metered pumping and measurement system for dispensing the required amount of one or more colorants into various sized containers of base. Computer-controlled dispensing machines have reached a level of sophistication so that only the code associated with a desired end color need be entered, and the machine draws from the associated memory in selecting the colorant(s) and volume(s) required for dispensing into the container of base paint.
Once filled with its complement of pigment dispersions, the dispensing machine may not be used for extended periods of time, i.e., from overnight to longer holiday periods. Furthermore, particular colors or types of pigment dispersions may not be frequently used.
Of principal concern in any such system is the ability to reproducibly and consistently obtain precisely the same shade and/or tint of mixed paint. Since the pigments in the colorant dispersions have a tendency to settle, the colorant reservoirs or canisters are typically equipped with intermittent stirrers, and the dispensing mechanism includes a recirculating loop that permits the pigment dispersion to be periodically pumped from the reservoir through the loop and returned to the reservoir.
However, a certain portion of the colorant dispersion can remain in the dispensing nozzle between the valve in the circulating loop and the nozzle orifice. In addition, the stirring and recirculating pump systems cannot totally prevent the separation and accumulation of pigments that have a tendency to settle from the colorant dispersions. However, even small changes in the composition of the colorant caused by settling or separation of the pigment dispersion can result in noticeable variations in custom tinted paints. Various measures have been proposed by dispensing machine designers to minimize the settling and drying of the pigment dispersions once they are loaded into the machines.
In U.S. Pat. No. 5,493,840, a circular trough containing water is positioned proximate the outlets of the dispensing nozzles for the purpose of providing an atmosphere that is high in water vapor in order to inhibit the drying of the colorant dispersion in the nozzles. This apparatus further complicates an already complex piece of equipment.
In order to reduce nozzle blockage, Canadian patent document 2,118,484 discloses a stem affixed to a valve, which in the closed position occupies the tip of the nozzle and also allows circulation of the pigment dispersion through a bypass port.
Since these mechanical features are not available for existing dispensing machines that have been in use for sometime, solutions to the problems of settling and nozzle blockage must be met by formulating the pigment dispersions sold for dispensing from these machines.
Universal colorant dispersions, i.e., those that are suitable for use with either aqueous or solvent-based surface coatings, have been well-known in the art for several decades. Universal pigment dispersions containing nacreous or pearlescent pigments are also well-known to the art. Nacreous pigments, i.e., pearlescent pigments, are used for decorative effect. The original "pearl essence" pigments were derived from fish scales and tissue. Limited supplies of this natural resource led to the development of nacreous basic lead carbonate in the 1930's. It is not known whether the natural product is commercially available today. Inorganic nacreous pigments are available in a variety of forms and are produced most commonly by coating a naturally occurring platelet of mica or other mineral clays with titanium dioxide, an iron oxide, or both. As used herein the terms "nacreous" and "pearlescent" are understood to be synonymous.
A wide variety of anti-settling or suspension agents have been employed in preparing pearlescent pigment oxide dispersions for use in surface coatings to reduce the tendency of the pigments to settle. Commercially acceptable formulations include at least three such agents. These suspension or anti-settling agents can include bentonite and other organo-clay mineral (hectorite) products, magnesium aluminum silicate and hydroxyethyl cellulose. The formulations employing these anti-settling agents are used for in-plant tinting of pre-mixed surface coatings where settling during shipment and storage prior to use is not a concern. This is because the shipping drums containing the pigment dispersions are equipped with efficient agitators that can maintain the dispersions as a reasonably uniform mixture and any remaining pigment can be scraped from the empty drum and added to the batch of base.
The number of colors of ready-mixed pearlescent paints must necessarily be limited by the costs of warehousing and retail shelf storage and display. Pearlescent pigment dispersions are also available in artist supply stores, but are sold only in small tubes and are relatively expensive.
A wide variety of chemical compounds have been developed for use as suspension agents and for preparing thixotropic compositions. For example, it is know from U.S. Pat. No. 5,270,399 to employ the synthetic silicate LAPONITE.RTM. RD, which is a thixotropic agent, in preparing finished surface coating compositions employing colored pigment dispersions in water dispersible base coat compositions.
It has also been known to use synthetic silicate compositions including those sold commercially under the trademark LAPONITE.RTM. in the automotive industry with metallic and pearlescent pigments. However, it is understood that the automotive finishes are also prepared in large batches that are comparable to the in-plant manufacture of surface coatings.
However, prior to this invention, it had been found that pearlescent colorant dispersions had a tendency to settle much more rapidly than conventional dispersions and efforts to produce a non-settling nacreous pigment dispersion were unsuccessful. For this reason, pearlescent dispersions have not been available for use in the dispensing machines used for in-store tinting.
Some of the advantages and capabilities that are provided by a universal machine dispensable pearlescent pigment include (1) ready availability to consumers and to the trade at an affordable price; (2) a greatly expanded range of colors and tints; (3) the availability of custom colors for use in connection with faux and fantasy finishing techniques for residential and commercial decorating or redecorating to achieve effects that have not heretofore been possible.
It is therefore an object of this invention to provide a non-settling, universal, machine dispensable pearlescent colorant dispersion.
It is a further object of the invention to provide a method and process for the manufacture of a non-settling, universal, machine dispensable pearlescent dispersion.
It is another object of the invention to provide a nacreous or pearlescent pigment dispersion that can be employed in existing dispensing machines used for the custom tinting of aqueous and solvent-thinned paint bases.
It is yet another object of this invention to provide such a dispersion and method for its manufacture that requires only one thixotropic agent to effect a non-settling nacreous pigment composition.
Another object of the invention is to provide a universal dispersion that contains no volatile organic content ("VOC"), as defined by current government environmental regulations.